Piezoelectric vibrator manufacturing method, piezoelectric vibrator, oscillator, electronic device, and radio-controlled timepiece

ABSTRACT

The piezoelectric vibrator includes: a package in which a first substrate and a second substrate are superimposed so as to form a cavity therebetween; outer electrodes which are formed on an outer surface of the first substrate; inner electrodes which are formed on the first substrate so as to be accommodated in the cavity; penetration electrodes which are formed so as to penetrate through the first substrate so that the outer electrodes and the inner electrodes are electrically connected; and a piezoelectric vibrating reed which is sealed in the cavity and electrically connected to the inner electrodes at the inner side of the cavity. The first substrate and the second substrate are bonded by a bonding film that is formed of a low-melting-point glass, and the bonding film is heated to a predetermined bonding temperature when the first substrate and the second substrate are bonded together, and is formed by being heated to a temperature higher than the bonding temperature before the bonding is performed.

RELATED APPLICATIONS

This application is a continuation of PCT/JP2008/071645 filed on Nov.28, 2008. The entire contents of this application is incorporated hereinby reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a method for forming a surface mounted device(SMD)-type piezoelectric vibrator in which a piezoelectric vibratingreed is sealed in a cavity formed between two bonded substrates, apiezoelectric vibrator manufactured by the manufacturing method, and anoscillator, an electronic device, and a radio-controlled timepiece eachhaving the piezoelectric vibrator.

2. Description of the Related Art

Recently, a piezoelectric vibrator utilizing quartz or the like has beenused in cellular phones and portable information terminals as the timesource, the timing source of a control signal, a reference signalsource, and the like. Although there are various piezoelectric vibratorsof this type, a surface mounted device-type piezoelectric vibrator isknown as one example thereof. As the main piezoelectric vibrator of thistype, generally, a three-layered piezoelectric vibrator in which apiezoelectric substrate having a piezoelectric vibrating reed formedthereon is interposed between the base substrate and a lid substratefrom above or below is known. In this case, the piezoelectric vibratingreed is accommodated in a cavity (sealed space) that is formed betweenthe base substrate and the lid substrate.

Moreover, in recent years, instead of the three-layered piezoelectricvibrator, a two-layered piezoelectric vibrator has also been developed.The piezoelectric vibrator of this type has a two-layered structure inwhich a base substrate and a lid substrate are directly bonded, and apiezoelectric vibrating reed is accommodated in a cavity formed betweenthe two substrates. The two-layered piezoelectric vibrator is ideallyused, as it is superior for achieving a thin profile compared with thethree-layered structure.

As a piezoelectric vibrator of this type, as disclosed in PatentDocument 1 as below, a configuration is known in which penetration holesare provided in a substrate (base substrate) formed of glass orceramics, a wiring metal is formed on the inner surfaces of thepenetration holes and the upper and lower surfaces around thepenetration holes or either of the surfaces, alloys are welded to thepenetration holes to form airtight terminals, and a crystal reed(piezoelectric vibrating reed) provided on the substrate surface iselectrically connected directly to the alloys of the airtight terminalsor through the wiring metal on the substrate surface. According to thisconfiguration, a predetermined driving voltage can be applied to thepiezoelectric vibrating reed from the outside of the piezoelectricvibrator through the airtight terminals, namely penetration electrodeswhich are electrodes formed so as to penetrate through the substrate.

Moreover, in the piezoelectric vibrator, the substrate and a cover (lidsubstrate) provided to the substrate are anodically bonded together byan anodic bonding metal film formed on the cover. As an example of anembodiment in which the substrate and the cover are anodically bondedtogether in such a way, a method is known in which a substrate and acover superimposed onto each other with a metal film disposedtherebetween are set on an electrode substrate of an anodic bondingmachine, and a predetermined bonding voltage is applied between themetal film and the electrode substrate. According to this method, it ispossible to cause an electrochemical reaction to occur at the interfacebetween the metal film and the substrate. As a result, the metal filmand the substrate are closely adhered tightly, whereby the substrate andthe cover are anodically bonded together.

Meanwhile, in piezoelectric vibrators, it is generally preferable tosuppress an equivalent resistance value (effective resistance value Re)to a low value. Since a piezoelectric vibrator having a low equivalentresistance value is capable of vibrating a piezoelectric vibrating reedwith a low power, a high-quality piezoelectric vibrator having highenergy efficiency can be achieved. Moreover, as the inside the cavity inwhich the piezoelectric reed is sealed approaches/is close to a vacuum,that is, as the degree of vacuum in the cavity increases, the equivalentresistance value can be suppressed to be lower is generally known.

-   Patent Document 1: JP-A-6-283951

However, the piezoelectric vibrator of the related art and themanufacturing method thereof have the following problems.

First, although the bonding film used for anodic bonding is generallyformed by photolithography, since the apparatus needed for thephotolithography is expensive, there is a problem in that bonding thebase substrate and the lid substrate by anodic bonding incurs largecosts.

Another problem is that when the base substrate and the lid substrateare bonded by anodic bonding, since a reaction gas mainly composed ofoxygen is generated when an electrochemical reaction occurs at theinterface between the bonding film and the substrate during the anodicbonding. Therefore, the reaction gas is sealed in the cavity by thebonding, and the degree of vacuum of the cavity decreases, whichinfluences the quality of the piezoelectric vibrator.

The invention has been made in view of the above problems, and an objectof the invention is to provide a high-quality, two-layered surfacemounted device-type piezoelectric vibrator which can be manufactured ata low cost and in which a decrease in the degree of vacuum in the cavityis suppressed and a method for manufacturing the piezoelectric vibrator.Moreover, another object of the invention is to provide an oscillator,an electronic device, and a radio-controlled timepiece each having thepiezoelectric vibrator.

SUMMARY OF THE INVENTION

The invention provides the following means in order to solve theproblems to attain the objects.

(1) The invention provides a method for manufacturing a piezoelectricvibrator including: a package in which a first substrate and a secondsubstrate are superimposed so as to form a cavity therebetween; outerelectrodes which are superimposed so as to form a cavity therebetween;outer electrodes which are formed on an outer surface of the firstsubstrate; inner electrodes which are formed on the first substrate soas to be accommodated in the cavity; penetration electrodes which areformed so as to penetrate through the first substrate so that the outerelectrodes and the inner electrodes are electrically connected; and apiezoelectric vibrating reed which is sealed in the cavity andelectrically connected to the inner electrodes at the inner side of thecavity, the method including: a bonding film forming step of forming abonding film on at least one of the first substrate and the secondsubstrate using a low-melting-point glass so as to bond the twosubstrates; a mounting step of electrically connecting the piezoelectricvibrating reed to the inner electrodes formed on the first substrate; aloading step of loading the first substrate and the second substrate ina vacuum chamber of which the inner pressure can be controlled after thebonding film forming step and the mounting step are performed; a heatingstep of heating the bonding film after the bonding film forming step andthe mounting step are performed; a depressurization step ofdepressurizing the inside of the vacuum chamber after the loading stepis performed; and a bonding step of superimposing the first substrateand the second substrate onto each other at the inner side of the vacuumchamber with the bonding film disposed therebetween while heating thebonding film to a predetermined bonding temperature to thereby bond thetwo substrates by the bonding film after the heating step and thedepressurization step are performed, wherein in the heating step, thebonding film is heated to a temperature higher than the bondingtemperature.

According to the manufacturing method, the bonding film is formed of alow-melting-point glass in the bonding film forming step. Therefore, thebonding film can be formed, for example, by screen printing and the likeas described above, and an expensive apparatus which is needed inphotolithography used in the related art in the process of forming thebonding film is not required. Thus, the piezoelectric vibrator can bemanufactured at a low cost.

Since organic materials, moisture, and the like are generally containedin the low-melting-point glass, when the bonding film is heated, theorganic material, moisture, and the like in the bonding film aredischarged to the outside as outgas.

Here, in the heating step, since the bonding film is heated to atemperature higher than the bonding temperature, outgas which will bedischarged from the bonding film when the bonding film is heated to thebonding temperature can be discharged in advance. Therefore, the outgasdischarged from the bonding film when the bonding film is heated to thebonding temperature in the bonding step which is performed later thanthe heating step can be suppressed to a very small amount.

Given the above, it is possible to suppress a decrease in the degree ofvacuum in the cavity by the outgas discharged from the bonding film.Thus, it is possible to manufacture the piezoelectric vibrator having afurther higher quality.

Moreover, when the depressurization step is performed later than theheating step, even if the outgas in the vacuum chamber is discharged inthe heating step performed later than the loading step, it is possibleto remove the outgas from the inside of the vacuum chamber. Thus, it ispossible to obtain the above-described operational effects morereliably.

(2) In the mounting step, the piezoelectric vibrating reed may bebump-bonded to the inner electrodes through gold bumps.

In this case, since the piezoelectric vibrating reed and the innerelectrodes are bump-bonded by the gold bumps, it is possible to securereliable conduction between the piezoelectric vibrating reed and theextraction electrodes and to manufacture the piezoelectric vibratorhaving high quality. In addition, since gold has a higher melting pointas compared to a conductive adhesive or the like which has been used formounting the piezoelectric vibrating reed, the gold bumps can reliablysupport the piezoelectric vibrating reed without being affected byheating even when the bonding film is heated to the bonding temperaturein the bonding step and when the bonding film is heated to a temperaturehigher than the bonding temperature in the heating step. Thus, it ispossible to manufacture the piezoelectric vibrator having a furtherhigher quality.

(3) The bonding temperature may be equal to or higher than 300° C.

In this case, since the bonding temperature is equal to or higher than300° C., even when the piezoelectric vibrator manufactured by themanufacturing method is mounted on other products as one componentusing, for example, a reflow method or the like which involves heating,it is possible to suppress generation of outgas. In this way, it ispossible to reliably suppress a decrease in the quality of thepiezoelectric vibrator when mounting the piezoelectric vibrator.

(4) The invention also provides a piezoelectric vibrator including: apackage in which a first substrate and a second substrate aresuperimposed so as to form a cavity therebetween; outer electrodes whichare formed on an outer surface of the first substrate; inner electrodeswhich are formed on the first substrate so as to be accommodated in thecavity; penetration electrodes which are formed so as to penetratethrough the first substrate so that the outer electrodes and the innerelectrodes are electrically connected; and a piezoelectric vibratingreed which is sealed in the cavity and electrically connected to theinner electrodes at the inner side of the cavity, wherein the firstsubstrate and the second substrate are bonded by a bonding film that isformed of a low-melting-point glass, and wherein the bonding film isheated to a predetermined bonding temperature when the first substrateand the second substrate are bonded together, and is formed by beingheated to a temperature higher than the bonding temperature before thebonding is performed.

According to the piezoelectric vibrator, since the bonding film isformed of a low-melting-point glass, it is possible to form the bondingfilm without using an expensive apparatus which is needed inphotolithography in the step of forming the bonding film and to form thepiezoelectric vibrator at a low cost. Moreover, since the bonding filmis heated to a temperature higher than the bonding temperature beforethe first substrate and the second substrate are bonded together, theoutgas which will be discharged from the bonding film when the bondingfilm is heated to the bonding temperature can be discharged in advance.Therefore, it is possible to suppress the outgas from being dischargedfrom the bonding film when the two substrates are bonded together tothereby suppress a decrease in the degree of vacuum of the cavity. Thus,it is possible to improve the quality of the piezoelectric vibrator.

(5) The piezoelectric vibrating reed may be bump-bonded to the innerelectrodes through gold bumps.

In this case, since the piezoelectric vibrating reed and the innerelectrodes are bump-bonded by the gold bumps, it is possible to securereliable conduction between the piezoelectric vibrating reed and theinner electrodes and to manufacture the piezoelectric vibrator havinghigh quality. In addition, since gold has a higher melting point ascompared to a conductive adhesive or the like which has been used formounting the piezoelectric vibrating reed, the gold bumps can reliablysupport the piezoelectric vibrating reed without being affected byheating even when the bonding film is heated. Thus, it is possible tofurther improve the quality of the piezoelectric vibrator.

(6) The invention also provides an oscillator in which the piezoelectricvibrator according to (4) or (5) is electrically connected to anintegrated circuit as an oscillating piece.

(7) The invention also provides an electronic device in which thepiezoelectric vibrator according to (4) or (5) is electrically connectedto a clock section.

(8) The invention also provides a radio-controlled timepiece in whichthe piezoelectric vibrator according to (4) or (5) is electricallyconnected to a filter section.

According to the oscillator, the radio-controlled timepiece, and theelectronic device, since they have the piezoelectric vibrator which canbe manufactured at a low cost and has a high quality, it is possible toachieve high quality and cost reductions.

According to the piezoelectric vibrator manufacturing method of theinvention, it is possible to manufacture a high-quality piezoelectricvibrator in which a decrease in the degree of vacuum in the cavity issuppressed and which can be manufactured at a low cost.

Moreover, according to the piezoelectric vibrator of the invention, itis possible to achieve high quality and cost reductions.

Furthermore, according to the oscillator, the electronic device, and theradio-controlled timepiece having the piezoelectric vibrator, it ispossible to achieve high quality and cost reductions.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing an external appearance of anexample of a piezoelectric vibrator according to an embodiment of theinvention.

FIG. 2 is a top view showing an inner structure of the piezoelectricvibrator shown in FIG. 1 when a piezoelectric vibrating reed is viewedfrom above with lid substrate removed.

FIG. 3 is a cross-sectional view of the piezoelectric vibrator takenalong the line A-A in FIG. 2.

FIG. 4 is an exploded perspective view of the piezoelectric vibratorshown in FIG. 1.

FIG. 5 is a top view of the piezoelectric vibrating reed thatconstitutes the piezoelectric vibrator shown in FIG. 1.

FIG. 6 is a bottom view of the piezoelectric vibrating reed shown inFIG. 5.

FIG. 7 is a cross-sectional view taken along the line B-B in FIG. 5.

FIG. 8 is a flowchart showing the flow of the manufacturing process ofthe piezoelectric vibrator shown in FIG. 1.

FIG. 9 is a view showing one step of the manufacturing process of thepiezoelectric vibrator in accordance with the flowchart shown in FIG. 8,showing a state where a plurality of recess portions and a bonding filmare formed on a lid substrate wafer serving as a base material of a lidsubstrate.

FIG. 10 is a view showing one step of the manufacturing process of thepiezoelectric vibrator in accordance with the flowchart shown in FIG. 8,showing a state where a bonding film and lead-out electrodes arepatterned on the upper surface of a base substrate wafer.

FIG. 11 is an overall view of the base substrate wafer in the stateshown in FIG. 10.

FIG. 12 is a view showing one step of the process of manufacturing thepiezoelectric vibrator in accordance with the flowchart shown in FIG. 8,and is a view showing a state where the base substrate wafer and the lidsubstrate wafer are loaded into a vacuum chamber.

FIG. 13 is a view showing one step of the process of manufacturing thepiezoelectric vibrator in accordance with the flowchart shown in FIG. 8,and is a view showing a state where the base substrate wafer and the lidsubstrate wafer are bonded together in the vacuum chamber.

FIG. 14 is a view showing one step of the process of manufacturing thepiezoelectric vibrator in accordance with the flowchart shown in FIG. 8,and is also an exploded perspective view of a wafer assembly in whichthe base substrate wafer and the lid substrate wafer are bonded with thepiezoelectric vibrating reed accommodated in a cavity.

FIG. 15 is a view showing the configuration of an oscillator accordingto an embodiment of the invention.

FIG. 16 is a view showing the configuration of an electronic deviceaccording to an embodiment of the invention.

FIG. 17 is a view showing the configuration of a radio-controlledtimepiece according to an embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(Piezoelectric Vibrator)

Hereinafter, an embodiment of a piezoelectric vibrator according to theinvention will be described with reference to the drawings.

In a piezoelectric vibrator 1 of the present embodiment, as shown inFIGS. 1 to 4, a base substrate (first substrate) 2 and a lid substrate(second substrate) 3 are laminated in two layers to form a box-likepackage 5. Moreover, the piezoelectric vibrator 1 is a surface mounteddevice-type piezoelectric vibrator in which a piezoelectric vibratingreed 4 is accommodated in a cavity C at the inner side of the package 5.

In FIG. 4, for better understanding of the drawings, illustrations ofthe excitation electrode 15, extraction electrodes 19 and 20, mountelectrodes 16 and 17, and weight metal film 21 described later areomitted.

As shown in FIGS. 5 to 7, the piezoelectric vibrating reed 4 is atuning-fork type vibrating reed which is formed of a piezoelectricmaterial such as crystal, lithium tantalate, or lithium niobate and isconfigured to vibrate when a predetermined voltage is applied thereto.

The piezoelectric vibrating reed 4 includes: a pair of vibrating arms 10and 11 disposed in parallel to each other; a base portion 12 to whichthe base end sides of the pair of vibrating arms 10 and 11 areintegrally fixed; an excitation electrode 15 which is formed on theouter surfaces of the pair of vibrating arms 10 and 11 so as to allowthe pair of vibrating arms 10 and 11 to vibrate and includes a firstexcitation electrode 13 and a second excitation electrode 14; and mountelectrodes 16 and 17 which are electrically connected to the firstexcitation electrode 13 and the second excitation electrode 14,respectively.

In addition, the piezoelectric vibrating reed 4 according to the presentembodiment is provided with groove portions 18 which are formed on bothprincipal surfaces of the pair of vibrating arms 10 and 11 along thelongitudinal direction of the vibrating arms 10 and 11. The grooveportions 18 are formed so as to extend from the base end sides of thevibrating arms 10 and 11 up to approximately the middle portionsthereof.

The excitation electrode 15 including the first excitation electrode 13and the second excitation electrode 14 is an electrode that allows thepair of vibrating arms 10 and 11 to vibrate at a predetermined resonancefrequency in a direction moving closer to or away from each other and ispatterned on the outer surfaces of the pair of vibrating arms 10 and 11in an electrically isolated state. Specifically, as shown in FIG. 7, thefirst excitation electrode 13 is mainly formed on the groove portion 18of one vibrating arm 10 and both side surfaces of the other vibratingarm 11. On the other hand, the second excitation electrode 14 is mainlyformed on both side surfaces of one vibrating arm 10 and the grooveportion 18 of the other vibrating arm 11.

Moreover, the first excitation electrode 13 and the second excitationelectrode 14 are electrically connected to the mount electrodes 16 and17 via the extraction electrodes 19 and 20, respectively, on bothprincipal surfaces of the base portion 12. A voltage is applied to thepiezoelectric vibrating reed 4 via the mount electrodes 16 and 17.

The above-mentioned excitation electrode 15, mount electrodes 16 and 17,and extraction electrodes 19 and 20 are formed by a coating of aconductive film of chromium (Cr), nickel (Ni), aluminum (Al), andtitanium (Ti), for example.

The tip ends of the pair of the vibrating arms 10 and 11 are coated witha weight metal film 21 for adjustment (frequency adjustment) of theirown vibration states in a manner such as to vibrate within apredetermined frequency range. The weight metal film 21 is divided intoa rough tuning film 21 a used for tuning the frequency roughly and afine tuning film 21 b used for tuning the frequency finely. By tuningthe frequency with the use of the rough tuning film 21 a and the finetuning film 21 b, the frequency of the pair of the vibrating arms 10 and11 can be set to fall within the range of the nominal frequency of thedevice.

The piezoelectric vibrating reed 4 configured in this way is bump-bondedto the upper surface of the base substrate 2 through gold bumps B asshown in FIGS. 3 and 4. More specifically, bump bonding is achieved in astate where the pair of mount electrodes 16 and 17 come into contactwith two gold bumps B formed on the lead-out electrodes 36 and 37,respectively, which are patterned on the upper surface of the basesubstrate 2. In this way, the piezoelectric vibrating reed 4 issupported in a state of being floated from the upper surface of the basesubstrate 2, and the mount electrodes 16 and 17 and the lead-outelectrodes 36 and 37 are electrically connected to each other.

The lid substrate 3 is a transparent insulating substrate formed of aglass material, for example, soda-lime glass, and is formed in aplate-like shape as shown in FIGS. 1, 3, and 4. A bonding surface sidethereof to be bonded to the base substrate 2 is formed with arectangular recess portion 3 a in which the piezoelectric vibrating reed4 is accommodated. The recess portion 3 a is a recess portion for acavity serving as the cavity C that accommodates the piezoelectricvibrating reed 4 when the two substrates 2 and 3 are superimposed oneach other. The lid substrate 3 is anodically bonded to the basesubstrate 2 in a state where the recess portion 3 a faces the basesubstrate 2.

The base substrate 2 is a transparent insulating substrate formed ofglass material, for example, soda-lime glass, similarly to the lidsubstrate 3, and is formed in a plate-like shape having a size capableof being superimposed on the lid substrate 3, as shown in FIGS. 1 to 4.

The base substrate 2 is formed with a pair of through-holes (penetrationholes) 30 and 31 penetrating through the base substrate 2. At this time,the pair of through-holes 30 and 31 is formed so as to be received inthe cavity C. More specifically, the through-holes 30 and 31 of thepresent embodiment are formed such that one through-hole 30 ispositioned close to the base portion 12 of the mounted piezoelectricvibrating reed 4, and the other through-hole 31 is positioned close tothe tip ends of the vibrating arms 10 and 11. In addition, although thepresent embodiment is described by way of an example of thethrough-holes which are configured to penetrate straight through thebase substrate 2, the invention is not limited to this example, but forexample, the through-holes may be formed in a tapered form whosediameter gradually decreases towards the lower surface of the basesubstrate 2. In any case, they only need to penetrate through the basesubstrate 2.

The pair of through-holes 30 and 31 is formed with a pair of penetrationelectrodes 32 and 33 which are formed so as to bury the through-holes 30and 31. The penetration electrodes 32 and 33 are formed of a conductivematerial such as Ag paste.

As shown in FIGS. 1 to 4, on the upper surface side of the basesubstrate 2 (the bonding surface side to be bonded to the lid substrate3), the pair of lead-out electrodes 36 and 37 is patterned by aconductive material (for example, aluminum) so as to be accommodated inthe cavity C.

The pair of lead-out electrodes 36 and 37 is patterned so that onepenetration electrode 32 of the pair of penetration electrodes 32 and 33is electrically connected to one mount electrode 16 of the piezoelectricvibrating reed 4, and the other penetration electrode 33 is electricallyconnected to the other mount electrode 17 of the piezoelectric vibratingreed 4.

More specifically, one lead-out electrode 36 is formed right above theone penetration electrode 32 to be disposed right below the base portion12 of the piezoelectric vibrating reed 4. Moreover, the other lead-outelectrode 37 is formed to be disposed right above the other penetrationelectrode 33 after being led out from a position near the one lead-outelectrode 36 towards the tip ends of the vibrating arms 10 and 11 alongthe vibrating arms 10 and 11.

Moreover, the gold bumps B are formed on the pair of lead-out electrodes36 and 37, and the piezoelectric vibrating reed 4 is mounted using thegold bumps B. In this way, the one mount electrode 16 of thepiezoelectric vibrating reed 4 is electrically connected to the onepenetration electrode 32 through the one lead-out electrode 36, and theother mount electrode 17 is electrically connected to the otherpenetration electrode 33 through the other lead-out electrode 37.

Moreover, on the lower surface of the base substrate 2, the outerelectrodes 38 and 39 are formed so as to be electrically connected tothe pair of penetration electrodes 32 and 33, respectively, as shown inFIGS. 1, 3, and 4. That is, one outer electrode 38 is electricallyconnected to the first excitation electrode 13 of the piezoelectricvibrating reed 4 via the one penetration electrode 32 and the onelead-out electrode 36. In addition, the other outer electrode 39 iselectrically connected to the second excitation electrode 14 of thepiezoelectric vibrating reed 4 via the other penetration electrode 33and the other lead-out electrode 37.

Moreover, in the present embodiment, as shown in FIGS. 1 to 4, the basesubstrate 2 and the lid substrate 3 are bonded by a bonding film 35formed of a low-melting-point glass. In the example shown in thefigures, the bonding film 35 is formed on the upper surface side of thebase substrate 2, and is formed along the peripheral edge of the basesubstrate 2 so as to surround the periphery of the recess portion 3 aformed on the lid substrate 3.

Moreover, in the present embodiment, the bonding film 35 is heated to apredetermined bonding temperature T when bonding the base substrate 2and the lid substrate 3 and is formed by being heated to a temperaturehigher than the bonding temperature T before the bonding is performed.This will be described in detail when describing the manufacturingmethod.

When the piezoelectric vibrator 1 configured in this manner is operated,a predetermined driving voltage is applied between the pair of outerelectrodes 38 and 39 formed on the base substrate 2. In this way, acurrent can be made to flow to the excitation electrode 15 including thefirst and second excitation electrodes 13 and 14, of the piezoelectricvibrating reed 4, and the pair of vibrating arms 10 and 11 are allowedto vibrate at a predetermined frequency in a direction moving closer toor away from each other. This vibration of the pair of vibrating arms 10and 11 can be used as the time source, the timing source of a controlsignal, the reference signal source, and the like.

(Piezoelectric Vibrator Manufacturing Method)

Next, a method for manufacturing a plurality of the above-describedpiezoelectric vibrators 1 at a time using a base substrate wafer 40 anda lid substrate wafer 50 will be described with reference to theflowchart shown in FIG. 8. Moreover, the piezoelectric vibratormanufacturing method according to the invention is not limited to amethod of using the lid substrate wafer 50 and the base substrate wafer40 described below. For example, one piezoelectric vibrator may bemanufactured at a time using a chip-shaped wafer of which the outerdimensions are made in advance to comply with the base substrate 2 andthe lid substrate 3 of the piezoelectric vibrator 1.

First, a piezoelectric vibrating reed manufacturing step is performed tomanufacture the piezoelectric vibrating reed 4 shown in FIGS. 5 to 7(S10). Moreover, after the piezoelectric vibrating reed 4 ismanufactured, rough tuning of a resonance frequency is performed. Thisrough tuning is achieved by irradiating the rough tuning film 21 a ofthe weight metal film 21 with a laser beam to partially evaporate therough tuning film 21 a, thus changing the weight thereof. Fine tuning ofadjusting the resonance frequency more accurately is performed after amounting step is performed. This fine tuning will be described later.

Subsequently, a first wafer manufacturing step is performed where a lidsubstrate wafer 50 later serving as the lid substrate 3 is manufacturedup to the stage immediately before bonding is achieved (S20). First, adisk-shaped lid substrate wafer 50 is formed by polishing a soda-limeglass to a predetermined thickness, cleaning the polished glass, andremoving the affected uppermost layer by etching or the like as shown inFIG. 9 (S21). After that, a recess forming step is performed where aplurality of recess portions 3 a to be used as a cavity is formed in amatrix form on the bonding surface of the lid substrate wafer 50 byetching or the like (S22). The first wafer manufacturing step ends atthis point.

Subsequently, at the same or a different time as the above-mentionedstep, a second wafer manufacturing step is performed where a basesubstrate wafer 40 later serving as the base substrate 2 is manufacturedup to the stage immediately before bonding is achieved (S30). First, adisk-shaped base substrate wafer 40 is formed by polishing a soda-limeglass to a predetermined thickness, cleaning the polished glass, andremoving the affected uppermost layer by etching or the like (S31).After that, a penetration electrode forming step is performed where aplurality of penetration electrodes 32 and 33 is formed on the basesubstrate wafer 40 (S32).

After that, as shown in FIG. 10, a bonding film forming step isperformed where the bonding film 35 is formed on the upper surface ofthe base substrate wafer 40 using a low-melting-point glass (S33). Atthat time, after a gel-like low-melting-point glass is printed on theupper surface of the base substrate wafer 40 at room temperature byscreen printing or the like, the glass is fused by baking and slowlycooled down to room temperature, whereby the bonding film 35 is formed.

Subsequently, as shown in FIGS. 10 and 11, a lead-out electrode formingstep is performed where a conductive material is patterned on the uppersurface of the base substrate wafer 40 so as to form a plurality oflead-out electrodes 36 and 37 which are electrically connected to eachpair of the penetration electrodes 32 and 33 (S34). In FIG. 11, forbetter understanding of the drawing, the illustration of the bondingfilm 35 is omitted.

The second wafer manufacturing step ends at this point.

In FIG. 8, although the lead-out electrode forming step (S34) isperformed after the bonding film forming step (S33), conversely, thebonding film forming step (S33) may be performed after the lead-outelectrode forming step (S34). The same operational effect can beobtained with any order of the steps. Therefore, the order of the stepsmay be appropriately changed according to need.

Subsequently, a mounting step is performed where a plurality ofmanufactured piezoelectric vibrating reeds 4 is bonded to the uppersurface of the base substrate wafer 40 with the lead-out electrodes 36and 37 disposed therebetween (S40). At that time, first, gold bumps Bare formed on the pair of lead-out electrodes 36 and 37. Moreover, thebase portion 12 of the piezoelectric vibrating reed 4 is placed on thegold bumps B, and thereafter, the piezoelectric vibrating reed 4 ispressed against the gold bumps B while heating the gold bumps B to apredetermined temperature. In this way, the piezoelectric vibrating reed4 is mechanically supported by the gold bumps B, and the mountelectrodes 16 and 17 are electrically connected to the lead-outelectrodes 36 and 37. Therefore, at this point, the pair of excitationelectrodes 15 of the piezoelectric vibrating reed 4 are electricallyconnected to the pair of penetration electrodes 32 and 33, respectively.

Particularly, since the piezoelectric vibrating reed 4 is bump-bonded,the piezoelectric vibrating reed 4 is supported in a state of beingfloated from the upper surface of the base substrate wafer 40.

Subsequently, as shown in FIG. 12, a loading step is performed where thelid substrate wafer 50 and the base substrate wafer 40 are loaded into avacuum chamber V of which the inner pressure can be controlled (S45).

Subsequently, a heating step is performed where the bonding film 35 isheated to a temperature higher than a bonding temperature T (S50). Here,the bonding temperature T is a temperature at which the bonding film 35is heated in a bonding step (S70) described later, and in the presentembodiment, the bonding temperature T is 300° C. That is, in the heatingstep, the bonding film 35 is heated for a predetermined period at atemperature higher than 300° C. Heating the bonding film 35 is notlimited to a case of heating only the bonding film 35 but also includesa case where the bonding film 35 is heated together with the basesubstrate wafer 40 on which the bonding film 35 is formed, etc.

Moreover, in the present embodiment, a pair of wafer clamping means (notshown) which is provided so as to face each other and be movable in adirection closer to or away from each other is provided in the vacuumchamber V. When the lid substrate wafer 50 and the base substrate wafer40 are loaded into the vacuum chamber V, as shown in FIG. 12, therespective wafers 40 and 50 are set on the respective wafer clampingmeans in a state where the upper surfaces of the respective wafers 40and 50 face each other and the two wafers 40 and 50 are separated fromeach other. Moreover, at that time, the respective wafers 40 and 50 maybe set on the wafer clamping means in a state where they are alignedusing reference marks or the like not shown as indices, for example.

Here, since organic materials, moisture, and the like are generallycontained in the low-melting-point glass, when the bonding film 35 isheated, the organic material, moisture, and the like in the bonding film35 are discharged to the outside as outgas. In this heating step, sincethe bonding film 35 is heated to a temperature higher than the bondingtemperature T, outgas which will be discharged from the bonding film 35when the bonding film 35 is heated to the bonding temperature T can bedischarged in advance.

Subsequently, a depressurization step is performed where the inside ofthe vacuum chamber V is depressurized (S60). In the present embodiment,a vacuum pump V1 which can control the inner pressure of the vacuumchamber V is provided in the vacuum chamber V, and the inside of thevacuum chamber V is depressurized by the vacuum pump V1. In this way,the outgas discharged in the heating step is removed from the inside ofthe vacuum chamber V.

Subsequently, as shown in FIG. 13, after the depressurization step, abonding step is performed where the lid substrate wafer 50 and the basesubstrate wafer 40 are bonded inside the vacuum chamber V by the bondingfilm 35 (S70). At that time, in the present embodiment, the bonding isachieved by superimposing the lid substrate wafer 50 and the basesubstrate wafer 40 onto each other with the bonding film 35 disposedtherebetween by moving the wafer clamping means closer to each otherwhile heating the bonding film 35 to 300° C. which is the bondingtemperature T. In addition, the bonding is achieved by the waferclamping means pressurizing the two wafers 40 and 50 so that the bondingfilm 35 is sandwiched between them. Moreover, in order to achievereliable bonding of the two wafers 40 and 50, the heating of the bondingfilm 35 at the bonding temperature T and the pressurization of the twowafers 40 and 50 are maintained for a predetermined period.

In this way, the piezoelectric vibrating reed 4 in which the two wafers40 and 50 are bonded and which is mounted on the base substrate wafer 40can be sealed in the cavity C which is formed between the two wafers 40and 50, and a wafer assembly 60 in which the base substrate wafer 40 andthe lid substrate wafer 50 are bonded to each other can be obtained. Thepredetermined period can be appropriately changed in accordance with thebonding temperature T, the force that pressurizes the two wafers 40 and50, the strain point of the low-melting-point glass used as the bondingfilm 35, and the like. Moreover, in FIG. 14, for better understanding ofthe drawing, the wafer assembly 60 is illustrated in an exploded state.Furthermore, the illustration of the bonding film 35 in the basesubstrate wafer 40 is omitted. The dotted line M shown in FIG. 14 is acutting line along which a cutting step performed later occurs.

Subsequently, the wafer assembly 60 is taken out of the vacuum chamberV, and an outer electrode forming step is performed where a conductivematerial is patterned onto the lower surface of the base substrate wafer40 so as to form a plurality of pairs of outer electrodes 38 and 39which is electrically connected to the pair of penetration electrodes 32and 33 (S80). Through this step, the piezoelectric vibrating reed 4which is sealed in the cavity C can be operated using the outerelectrodes 38 and 39.

Subsequently, a fine tuning step is performed on the wafer assembly 60where the frequencies of the individual piezoelectric vibrators 1 sealedin the cavities C are tuned finely to fall within a predetermined range(S90). Specifically, a voltage is applied to the pair of outerelectrodes 38 and 39 which are formed on the lower surface of the basesubstrate wafer 40, thus allowing the piezoelectric vibrating reeds 4 tovibrate. A laser beam is irradiated onto the lid substrate wafer 50 fromthe outer side while measuring the vibration frequencies to evaporatethe fine tuning film 21 b of the weight metal film 21. In this way,since the weight on the tip end sides of the pair of vibrating arms 10and 11 is changed, the fine tuning can be performed in such a way thatthe frequency of the piezoelectric vibrating reed 4 falls within thepredetermined range of the nominal frequency.

After the fine tuning of the frequency is completed, a cutting step isperformed where the bonded wafer assembly 60 is cut along the cuttingline M shown in FIG. 14 to obtain small fragments (S100). As a result, aplurality of two-layered surface mounted device-type piezoelectricvibrators 1 shown in FIG. 1, in which the piezoelectric vibrating reed 4is sealed in the cavity C formed between the base substrate 2 and thelid substrate 3 being bonded together, can be manufactured at a time.

The fine tuning step (S90) may be performed after performing the cuttingstep (S100) to obtain the individual fragmented piezoelectric vibrators1. However, as described above, by performing the fine tuning step (S90)earlier, since the fine tuning step can be performed on the waferassembly 60, it is possible to perform the fine tuning on the pluralityof piezoelectric vibrators 1 more efficiently. Therefore, it isdesirable because throughput can be increased.

Subsequently, an inner electrical property test is conducted (S110).That is, the resonance frequency, resonance resistance value, drivelevel properties (the excitation power dependence of the resonancefrequency and the resonance resistance value), and the like of thepiezoelectric vibrating reed 4 are measured and checked. Moreover, theinsulation resistance properties and the like are checked as well.Finally, an external appearance test of the piezoelectric vibrator 1 isconducted to check the dimensions, the quality, and the like. In thisway, the manufacturing of the piezoelectric vibrator 1 ends.

As described above, in the piezoelectric vibrator manufacturing methodaccording to the present embodiment, the bonding film 35 is formed of alow-melting-point glass in the bonding film forming step. Therefore, thebonding film 35 can be formed, for example, by screen printing and thelike as described above, and an expensive apparatus which is needed inphotolithography used in the related art in the process of forming thebonding film 35 is not required. Thus, the piezoelectric vibrator 1 canbe manufactured at a low cost.

In addition, the bonding step is performed inside the vacuum chamber Vafter the depressurization step, that is, the bonding step is performedlater than the heating step. Therefore, since the outgas discharged fromthe bonding film 35 when being heated to the bonding temperature in thebonding step can be suppressed to a very small amount, it is possible tosuppress a decrease in the degree of vacuum in the cavity C by theoutgas discharged from the bonding film 35. Thus, it is possible tomanufacture the piezoelectric vibrator 1 having high quality.

Furthermore, since the piezoelectric vibrating reed 4 and the lead-outelectrodes 36 and 37 are bump-bonded by the gold bumps B, it is possibleto secure reliable conduction between the piezoelectric vibrating reed 4and the lead-out electrodes 36 and 37 and to manufacture thepiezoelectric vibrator 1 having high quality. In addition, since goldhas a higher melting point as compared to a conductive adhesive or thelike which has been used for mounting the piezoelectric vibrating reed4, the gold bumps can reliably support the piezoelectric vibrating reed4 without being affected by heating even when the bonding film 35 isheated to the bonding temperature T in the bonding step, and the bondingfilm 35 is heated to a temperature higher than the bonding temperature Tin the heating step. Thus, it is possible to manufacture thepiezoelectric vibrator 1 having a further higher quality.

In addition, since the bonding temperature T in the bonding step isequal to or higher than 300° C., even when the piezoelectric vibrator 1manufactured by the manufacturing method is mounted on other products asone component using, for example, a reflow method or the like whichinvolves heating, it is possible to suppress generation of outgas. Inthis way, it is possible to reliably suppress a decrease in the qualityof the piezoelectric vibrator 1 when mounting the piezoelectric vibrator1.

(Oscillator)

Next, an embodiment of an oscillator according to the invention will bedescribed with reference to FIG. 15. FIG. 15 is a diagram showing aconfiguration of an oscillator having the piezoelectric vibrator 1.

As shown in FIG. 15, an oscillator 100 according to the presentembodiment is one in which the piezoelectric vibrator 1 is configured asan oscillating piece electrically connected to an integrated circuit101. The oscillator 100 includes a substrate 103 on which an electroniccomponent 102, such as a capacitor, is mounted. The integrated circuit101 for an oscillator is mounted on the substrate 103, and thepiezoelectric vibrator 1 is mounted near the integrated circuit 101. Theelectronic component 102, the integrated circuit 101, and thepiezoelectric vibrator 1 are electrically connected to each other by awiring pattern (not shown). In addition, each of the constituentcomponents is molded with a resin (not shown).

In the oscillator 100 configured as described above, when a voltage isapplied to the piezoelectric vibrator 1, the piezoelectric vibratingreed 4 in the piezoelectric vibrator 1 vibrates. This vibration isconverted into an electrical signal due to the piezoelectric property ofthe piezoelectric vibrating reed 4 and is then input to the integratedcircuit 101 as the electrical signal. The input electrical signal issubjected to various kinds of processing by the integrated circuit 101and is then output as a frequency signal. In this way, the piezoelectricvibrator 1 functions as an oscillating piece.

Moreover, by selectively setting the configuration of the integratedcircuit 101, for example, an RTC (Real Time Clock) module, according todemand, it is possible to add a function of controlling the operationdate or time of the corresponding device or an external device or ofproviding the time or calendar in addition to a single functionaloscillator for a clock.

As described above, according to the oscillator 100 of the presentembodiment, since the oscillator 100 includes the piezoelectric vibrator1 which can be manufactured at a low cost and with a high quality, theoscillator 100 itself can be manufactured at a low cost and with a highquality.

(Electronic Device)

Next, an embodiment of an electronic device according to the inventionwill be described with reference to FIG. 16. In addition, a portableinformation device including the piezoelectric vibrator 1 will bedescribed as an example of an electronic device. The portableinformation device 110 according to the present embodiment isrepresented by a mobile phone, for example, and has been developed andimproved from a wristwatch in the related art. The portable informationdevice 110 is similar to a wristwatch in external appearance, and aliquid crystal display is disposed in a portion equivalent to a dial padso that a current time and the like can be displayed on this screen.Moreover, when it is used as a communication apparatus, it is possibleto remove it from the wrist and to perform the same communication as amobile phone in the related art with a speaker and a microphone built inan inner portion of the band. However, the portable information device110 is very small and light compared with a mobile phone in the relatedart.

Next, the configuration of the portable information device 110 accordingto the present embodiment will be described. As shown in FIG. 16, theportable information device (electronic device) 110 includes thepiezoelectric vibrator 1 and a power supply section 111 for supplyingpower. The power supply section 111 is formed of a lithium secondarybattery, for example. A control section 112 which performs various kindsof control, a clock section 113 which performs counting of time and thelike, a communication section 114 which performs communication with theoutside, a display section 115 which displays various kinds ofinformation, and a voltage detecting section 116 which detects thevoltage of each functional section are connected in parallel to thepower supply section 111. In addition, the power supply section 111supplies power to each functional section.

The control section 112 controls an operation of the entire system. Forexample, the control section 112 controls each functional section totransmit and receive the audio data or to measure or display a currenttime. In addition, the control section 112 includes a ROM in which aprogram is written in advance, a CPU which reads and executes a programwritten in the ROM, a RAM used as a work area of the CPU, and the like.

The clock section 113 includes an integrated circuit, which has anoscillation circuit, a register circuit, a counter circuit, and aninterface circuit therein, and the piezoelectric vibrator 1. When avoltage is applied to the piezoelectric vibrator 1, the piezoelectricvibrating reed 4 vibrates, and this vibration is converted into anelectrical signal due to the piezoelectric property of the piezoelectricvibrating reed 4 and is then input to the oscillation circuit as theelectrical signal. The output of the oscillation circuit is binarized tobe counted by the register circuit and the counter circuit. Then, asignal is transmitted to or received from the control section 112through the interface circuit, and current time, current date, calendarinformation, and the like are displayed on the display section 115.

The communication section 114 has the same function as a mobile phone inthe related art, and includes a wireless section 117, an audioprocessing section 118, a switching section 119, an amplifier section120, an audio input/output section 121, a telephone number input section122, a ring tone generating section 123, and a call control memorysection 124.

The wireless section 117 transmits/receives various kinds of data, suchas audio data, to/from the base station through an antenna 125. Theaudio processing section 118 encodes and decodes an audio signal inputfrom the wireless section 117 or the amplifier section 120. Theamplifier section 120 amplifies a signal input from the audio processingsection 118 or the audio input/output section 121 up to a predeterminedlevel. The audio input/output section 121 is formed by a speaker, amicrophone, and the like, and amplifies a ring tone or incoming sound orcollects the sound.

In addition, the ring tone generating section 123 generates a ring tonein response to a call from the base station. The switching section 119switches the amplifier section 120, which is connected to the audioprocessing section 118, to the ring tone generating section 123 onlywhen a call arrives, so that the ring tone generated in the ring tonegenerating section 123 is output to the audio input/output section 121through the amplifier section 120.

In addition, the call control memory section 124 stores a programrelated to incoming and outgoing call control for communications.Moreover, the telephone number input section 122 includes, for example,numeric keys from 0 to 9 and other keys. The user inputs a telephonenumber of a communication destination and the like by pressing thesenumeric keys and the like.

The voltage detecting section 116 detects a voltage drop when a voltage,which is applied from the power supply section 111 to each functionalsection, such as the control section 112, drops below the predeterminedvalue, and notifies the control section 112 of the detection of thevoltage drop. In this case, the predetermined voltage value is a valuewhich is set beforehand as the lowest voltage necessary to operate thecommunication section 114 stably. For example, it is about 3 V. When thevoltage drop is notified from the voltage detecting section 116, thecontrol section 112 disables the operation of the wireless section 117,the audio processing section 118, the switching section 119, and thering tone generating section 123. In particular, the operation of thewireless section 117 that consumes a large amount of power should benecessarily stopped. In addition, a message informing the user that thecommunication section 114 is not available due to insufficient batterypower is displayed on the display section 115.

That is, it is possible to disable the operation of the communicationsection 114 and display the notice on the display section 115 by thevoltage detecting section 116 and the control section 112. This messagemay be a character message. Or as a more intuitive indication, a crossmark (X) may be displayed on a telephone icon displayed at the top ofthe display screen of the display section 115.

In addition, the function of the communication section 114 can be morereliably stopped by providing a power shutdown section 126 capable ofselectively shutting down the power to a section related to the functionof the communication section 114.

As described above, according to the portable information device 110 ofthe present embodiment, since the portable information device 110includes the piezoelectric vibrator 1 which can be manufactured at a lowcost and with a high quality, the portable information device 110 itselfcan be manufactured at a low cost and with a high quality.

(Radio-Controlled Timepiece)

Next, a radio-controlled timepiece according to still another embodimentof the invention will be described with reference to FIG. 17. FIG. 17 isa diagram showing a configuration of a radio-controlled timepiece havingthe piezoelectric vibrator 1 described above.

As shown in FIG. 17, a radio-controlled timepiece 130 according to thepresent embodiment includes the piezoelectric vibrators 1 electricallyconnected to a filter section 131. The radio-controlled timepiece 130 isa clock with a function of receiving a standard radio wave including theclock information, automatically changing it to the correct time, anddisplaying the correct time.

In Japan, there are transmission centers (transmission stations) thattransmit a standard radio wave in Fukushima Prefecture (40 kHz) and SagaPrefecture (60 kHz), and each center transmits the standard radio wave.A long wave with a frequency of, for example, 40 kHz or 60 kHz has botha characteristic of propagating along the land surface and acharacteristic of propagating while being reflected between theionosphere and the land surface, and therefore has a propagation rangewide enough to cover the entire area in Japan through the twotransmission centers.

The functional configuration of the radio-controlled timepiece 130 willbe described with reference to FIG. 17.

An antenna 132 receives a long standard radio wave with a frequency of40 kHz or 60 kHz. The long standard radio wave is obtained by performingAM modulation of the time information, which is called a time code,using a carrier wave with a frequency of 40 kHz or 60 kHz. The receivedlong standard wave is amplified by an amplifier 133 and is then filteredand synchronized by the filter section 131 having the plurality ofpiezoelectric vibrators 1.

In the present embodiment, the piezoelectric vibrators 1 includepiezoelectric vibrator sections 134 and 135 having resonance frequenciesof 40 kHz and 60 kHz, respectively, which are the same frequencies asthe carrier frequency.

In addition, the filtered signal with a predetermined frequency isdetected and demodulated by a detection and rectification circuit 136.Then, the time code is extracted by a waveform shaping circuit 137 andcounted by the CPU 138. The CPU 138 reads the information including thecurrent year, the total number of days, the day of the week, the time,and the like. The read information is reflected on an RTC 139, and thecorrect time information is displayed.

Because the carrier wave is 40 kHz or 60 kHz, a vibrator having thetuning-fork structure described above is suitable for the piezoelectricvibrator sections 134 and 135.

Moreover, although the above explanation has been given for the case inJapan, the frequency of a long standard wave is different in othercountries. For example, a standard wave of 77.5 kHz is used in Germany.Therefore, when the radio-controlled timepiece 130 which is alsooperable in other countries is assembled in a portable device, thepiezoelectric vibrator 1 corresponding to frequencies different from thefrequencies used in Japan is necessary.

As described above, according to the radio-controlled timepiece 130 ofthe present embodiment, since the radio-controlled timepiece 130includes the piezoelectric vibrator 1 which can be manufactured at a lowcost and with a high quality, the radio-controlled timepiece 130 itselfcan be manufactured at a low cost and with a high quality.

It should be noted that the technical scope of the invention is notlimited to the embodiments above, and the invention can be modified invarious ways without departing from the spirit of the invention.

For example, although the above-described embodiments have beendescribed by way of an example of the grooved piezoelectric vibratingreed 4 in which the groove portions 18 are formed on both surfaces ofthe vibrating arms 10 and 11 as an example of the piezoelectricvibrating reed 4, the piezoelectric vibrating reed 4 may be a type ofpiezoelectric vibrating reed without the groove portions 18. However,since the field efficiency between the pair of the excitation electrodes15 when a predetermined voltage is applied to the pair of excitationelectrodes 15 can be increased by forming the groove portions 18, it ispossible to suppress the vibration loss further and to improve thevibration properties much more. That is to say, it is possible todecrease the CI value (crystal impedance) further and to improve theperformance of the piezoelectric vibrating reed 4 further. In thisrespect, it is preferable to form the groove portions 18.

In addition, although the embodiment has been described by way of anexample of a tuning-fork type piezoelectric vibrating reed 4, thepiezoelectric vibrating reed of the invention is not limited to thetuning-fork type piezoelectric vibrating reed but may be athickness-shear type piezoelectric vibrating reed, for example.

In addition, in the embodiment, although the cavity C is formed byproviding the recess portion 3 a in the lid substrate 3, the inventionis not limited to this, and for example, the cavity C may be formed byproviding the recess portion in the base substrate 2, and the cavity Cmay be formed by providing the recess portions in the two substrates 2and 3.

In addition, in the embodiment, although the bonding film 35 is formedon the base substrate 2, the invention is not limited to this, and thebonding film may be formed on the lid substrate 3, and the bonding filmmay be formed on the two substrates 2 and 3.

In addition, in the embodiment, although the piezoelectric vibratingreed 4 is bonded to the lead-out electrodes 36 and 37 by the gold bumpsB, the invention is not limited to the gold bumps B.

In addition, in the embodiment, although the bonding temperature T inthe bonding step is 300° C., the invention is not limited to this.However, the bonding temperature T is preferably equal to or higher than300° C. In addition, when a crystal is used as the piezoelectricvibrating reed 4, the bonding temperature T is preferably at least lowerthan a phase transition temperature which is a transition pointassociated with the piezoelectric properties of a crystal.

In addition, in the embodiment, although the piezoelectric vibrator 1 ismanufactured in the order of the mounting step (S40), the loading step(S45), the heating step (S50), and the depressurization step (S60), theinvention is not limited to this. The loading step (S45) and the heatingstep (S50) may only need to be performed later than the mounting step(S40), and the depressurization step (S60) may only need to be performedlater than the loading step (S45). For example, the piezoelectricvibrator may be manufactured in the order of the mounting step (S40),the heating step (S50), the loading step (S45), and the depressurizationstep (S60), and the piezoelectric vibrator may be manufactured in theorder of the mounting step (S40), the loading step (S45), thedepressurization step (S60), and the heating step (S50).

In addition, within a range not deviating from the object of theinvention, constituent elements of the above-described embodiments maybe appropriately substituted with well-known constituent elements, andthe above-described modified examples may be appropriately combined.

What is claimed is:
 1. A method for manufacturing a piezoelectricvibrator comprising: a package in which a first substrate and a secondsubstrate are superimposed so as to form a cavity therebetween; outerelectrodes which are formed on an outer surface of the first substrate;inner electrodes which are formed on the first substrate so as to beaccommodated in the cavity; penetration electrodes which are formed soas to penetrate through the first substrate so that the outer electrodesand the inner electrodes are electrically connected; and a piezoelectricvibrating reed which is sealed in the cavity and electrically connectedto the inner electrodes at the inner side of the cavity, the methodcomprising: a bonding film forming step of forming a bonding film on atleast one of the first substrate and the second substrate using alow-melting-point glass so as to bond the two substrates; a mountingstep of electrically connecting the piezoelectric vibrating reed to theinner electrodes formed on the first substrate; a loading step ofloading the first substrate and the second substrate in a vacuum chamberof which the inner pressure can be controlled after the bonding filmforming step and the mounting step are performed; a heating step ofheating the bonding film after the bonding film forming step and themounting step are performed; a depressurization step of depressurizingthe inside of the vacuum chamber after the loading step is performed;and a bonding step of superimposing the first substrate and the secondsubstrate onto each other at the inner side of the vacuum chamber withthe bonding film disposed therebetween while heating the bonding film toa predetermined bonding temperature to thereby bond the two substratesby the bonding film after the heating step and the depressurizing stepare performed, wherein in the heating step, the bonding film is heatedto a temperature higher than the bonding temperature.
 2. The method formanufacturing the piezoelectric vibrator according to claim 1, whereinin the mounting step, the piezoelectric vibrating reed is bump-bonded tothe inner electrodes through gold bumps.
 3. The method for manufacturingthe piezoelectric vibrator according to claim 1, wherein the bondingtemperature is equal to or higher than 300° C.
 4. A piezoelectricvibrator comprising: a package in which a first substrate and a secondsubstrate are superimposed so as to form a cavity therebetween; outerelectrodes which are formed on an outer surface of the first substrate;inner electrodes which are formed on the first substrate so as to beaccommodated in the cavity; penetration electrodes which are formed soas to penetrate through the first substrate so that the outer electrodesand the inner electrodes are electrically connected; and a piezoelectricvibrating reed which is sealed in the cavity and electrically connectedto the inner electrodes at the inner side of the cavity, wherein thefirst substrate and the second substrate are bonded by a bonding filmthat is formed of a low-melting-point glass, and wherein the bondingfilm is heated to a predetermined bonding temperature when the firstsubstrate and the second substrate are bonded together, and is formed bybeing heated to a temperature higher than the bonding temperature beforethe bonding is performed.
 5. The piezoelectric vibrator according toclaim 4, wherein the piezoelectric vibrating reed is bump-bonded to theinner electrodes through gold bumps.
 6. An oscillator in which thepiezoelectric vibrator according to claim 4 is electrically connected toan integrated circuit as an oscillating piece.
 7. An electronic devicein which the piezoelectric vibrator according to claim 4 is electricallyconnected to a clock section.
 8. A radio-controlled timepiece in whichthe piezoelectric vibrator according to claim 4 is electricallyconnected to a filter section.